$green = #02a774;
$yellow = #F5A100;
$bc = #e4e4e4;
// 一像素下边框
bottom-border-1px($color)
 position relative
 border none
 &:after
  content ''
  position absolute
  left 0
  bottom 0
  width 100%
  height 1px
  background-color $color
  transform scaleY(0.5)
// 一像素上边框
top-border-1px($color)
 position relative
 &::before
  content ''
  position absolute
  z-index 200
  left 0
  top 0
  width 100%
  height 1px
  background-color $color
//根据像素比缩放 1px 像素边框
@media only screen and (-webkit-device-pixel-ratio: 2 )
 .border-1px
  &::before
   transform scaleY(.5)
@media only screen and (-webkit-device-pixel-ratio: 3 )
 .border-1px
   &::before
     transform scaleY(.333333)
//根据像素比来使用 2x 图 3x 图
bg-image($url)
 background-image: url($url + "@2x.png")
@media (-webkit-min-device-pixel-ratio: 3),(min-device-pixel-ratio: 3)
 background-image: url($url + "@3x.png")
//清除浮动
 clearFix()
  *zoom 1
  &::after
     content ''
     display block
     clear both
